Method for determining the exhaust pressure of an engine

Abstract

The present invention provides a method for determining an engine's exhaust pressure, comprising the following steps: obtaining the flow rate, flow area, and flow coefficient of an equivalent nozzle, as well as the upstream temperature and the pressure ratio of the downstream pressure to the upstream pressure of the equivalent nozzle. The equivalent nozzle is a nozzle model established based on the exhaust pipe structure. The upstream pressure of the equivalent nozzle is determined based on the flow rate, upstream temperature, flow area, flow coefficient, and pressure ratio. The exhaust pressure is determined based on the upstream pressure of the equivalent nozzle. By introducing influencing factors such as the flow cross-section and flow coefficient, the correct calculation of hot exhaust gas in the engine cylinder, and thus the correct calculation of the fresh charge, is ensured, providing accurate input for the engine's fuel consumption, emissions, safety, and power performance.

Description

Technical Field

[0001] The present invention relates to the field of automobiles, and in particular to a method for determining the exhaust pressure of an engine. Background Art

[0002] The accuracy of engine exhaust pressure directly determines the accuracy of residual exhaust gas calculations within the engine cylinder, which in turn affects the accuracy of fresh charge in the cylinder. This in turn influences engine control parameters such as ignition and fuel injection, ultimately impacting engine fuel consumption, emissions, and safety. For turbocharged engines, exhaust pressure accuracy also affects the accuracy of boost control, which in turn affects engine power response. Therefore, accurate exhaust pressure calculation is crucial for ensuring engine fuel consumption, emissions, safety, and power.

[0003] Exhaust pressure is mainly divided into the pressure before the catalyst package Pcat and the pressure before the turbine Pexh. For non-supercharged engines, the exhaust pressure mainly refers to the pressure before the catalyst package. The present invention is explained using a supercharged engine as an example, but is not limited to supercharged engines.

[0004] The current mainstream calculation strategy for exhaust pressure simplifies the pre-turbulence pressure into a function of exhaust flow and exhaust temperature, as shown in formula (1), and calculates the pre-turbulence pressure by looking up the flow and temperature tables; the calculation of the pre-turbulence pressure is simplified to the pre-turbulence pressure, exhaust flow and boost pressure ratio π in function, as shown in formula (2).

[0005] P cat =f(m,T) (1)

[0006] P exh =f(P cat ,m,π in ) (2)

[0007] The above algorithm has reasonable accuracy for gasoline engines that meet the National V emission regulations and those before the National V emission regulations. However, as emission and fuel consumption regulations become increasingly stringent, particulate filters (GPFs) and variable geometry turbochargers (VGTs) are increasingly used in gasoline engines. The traditional mainstream exhaust pressure algorithm will produce large errors due to its oversimplification. Summary of the Invention

[0008] The present invention aims to solve the problem of large errors in the mainstream exhaust pressure algorithm in the prior art. It provides a method for determining the exhaust pressure of an engine, which improves the accuracy of exhaust pressure calculation by introducing the influence factors of flow cross section and flow coefficient.

[0009] A method for determining the exhaust pressure of an engine is provided, comprising the steps of:

[0010] Obtain the flow rate, flow area and flow coefficient of the equivalent nozzle, as well as the upstream temperature and the pressure ratio of the downstream pressure to the upstream pressure of the equivalent nozzle. The equivalent nozzle is a nozzle model established based on the exhaust pipe structure; determine the upstream pressure of the equivalent nozzle based on the flow rate, upstream temperature, flow area, flow coefficient and pressure ratio; and determine the exhaust pressure based on the upstream pressure of the equivalent nozzle.

[0011] According to another specific embodiment of the present invention, an embodiment of the present invention discloses a method for determining the exhaust pressure of an engine, wherein determining the upstream pressure includes:

[0012]

[0013] Where:

[0014] P1 is the upstream pressure of the equivalent nozzle;

[0015] dm / dt is the flow rate;

[0016] f(T1) is the upstream temperature function obtained based on the upstream temperature and the gas constant of the fuel gas;

[0017] f(μ1) is the flow coefficient function obtained based on the flow coefficient;

[0018] f(F res ) is a flow area function obtained based on the flow area;

[0019] ψ is the piecewise pressure ratio function obtained according to the pressure ratio.

[0020] According to another specific embodiment of the present invention, an embodiment of the present invention discloses a method for determining the exhaust pressure of an engine, in which a comparison table is prepared in advance based on the correspondence between the segmented pressure ratio function and the pressure ratio of the upstream and downstream of the equivalent nozzle. When actually controlling the engine, the value of the segmented pressure ratio function corresponding to the pressure ratio is obtained by looking up the comparison table.

[0021] Among them, the segmented pressure ratio function satisfies the relationship:

[0022]

[0023] Where:

[0024] P0 is the downstream pressure;

[0025] k is the isentropic index.

[0026] According to another specific embodiment of the present invention, an embodiment of the present invention discloses a method for determining the exhaust pressure of an engine, wherein the flow coefficient function is f(μ1)=1 / μ1, where μ1 is the flow coefficient of the equivalent nozzle.

[0027] According to another specific embodiment of the present invention, an embodiment of the present invention discloses a method for determining the exhaust pressure of an engine, wherein the flow coefficient is obtained according to the pressure ratio, and the flow coefficient and the pressure ratio satisfy the relationship:

[0028] μ1=a1+a2*π-a3*π 2 , where π = P0 / P1, and coefficients a1, a2, and a3 are calibrated and fitted according to the actual engine performance.

[0029] According to another specific embodiment of the present invention, an embodiment of the present invention discloses a method for determining the exhaust pressure of an engine, wherein the flow area function is f(F res )=1 / F res , where F res is the circulation area; and

[0030] If the engine does not have a particulate filter, the flow area function is a fixed value.

[0031] If the engine has a particulate filter, the flow area function is obtained by looking up the accumulated carbon amount table according to the accumulated carbon amount of the particulate filter. The accumulated carbon amount table is pre-calculated based on the engine's running time and the soot generated.

[0032] If the engine has a turbocharger, the flow area function is obtained by looking up the table based on the turbine nozzle ring angle.

[0033] According to another specific embodiment of the present invention, an embodiment of the present invention discloses a method for determining the exhaust pressure of an engine, wherein the upstream temperature function

[0034] Where:

[0035] R is the fuel gas constant;

[0036] T1 is the upstream temperature.

[0037] According to another specific embodiment of the present invention, an embodiment of the present invention discloses a method for determining the exhaust pressure of an engine. If the engine is in a steady-state operating condition, the flow rate is the intake flow rate plus the fuel mass flow rate, wherein the intake flow rate is measured by a flow meter installed in the intake pipe, and the fuel mass flow rate is calculated based on the intake flow rate, the air-fuel ratio, and the excess air coefficient;

[0038] If the engine is in dynamic operation, the flow rate is determined by the available cycle air mass plus the fuel mass divided by the cycle time.

[0039] According to another specific embodiment of the present invention, an embodiment of the present invention discloses a method for determining the exhaust pressure of an engine. If the engine has a particulate filter, a nozzle model is established with the particulate filter as a first equivalent nozzle, and the exhaust pressure includes a pressure before the catalytic package, which is the upstream pressure of the first equivalent nozzle.

[0040] If the engine has a particulate filter and a turbocharger, the nozzle models are established with the particulate filter and the turbocharger as the first equivalent nozzle and the second equivalent nozzle, respectively. The exhaust pressure includes the pressure before the catalyst package and the pressure before the turbine. The pressure before the catalyst package is the upstream pressure of the first equivalent nozzle, and the pressure before the turbine is the upstream pressure of the second equivalent nozzle.

[0041] According to another specific embodiment of the present invention, an embodiment of the present invention discloses a method for determining the exhaust pressure of an engine, wherein the downstream pressure of a first equivalent nozzle is atmospheric pressure. The downstream pressure of a second equivalent nozzle is directly obtained by a sensor. Alternatively, if the engine has a particulate filter and a variable geometry turbocharger, the downstream pressure of the second equivalent nozzle is the upstream pressure of the first equivalent nozzle.

[0042] The beneficial effects of the present invention are:

[0043] The amount of hot exhaust gas in the cylinder affects the temperature of the mixture after the intake valve closes. Excessively high mixture temperature can cause compression ignition during the compression stroke of a spark-ignition gasoline engine, causing a sharp increase in the pressure rise rate and damaging the crankshaft connecting rod mechanism. This invention aims to provide a more accurate exhaust pressure calculation strategy that incorporates the influence of the flow cross-section and flow coefficient to ensure accurate calculation of the hot exhaust gas in the engine cylinder, and thus the fresh charge, providing accurate input for engine fuel consumption, emissions, safety, and power performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 Schematic diagram of the model structure of an equivalent nozzle in a method for determining the exhaust pressure of an engine according to an embodiment of the present invention;

[0045] Figure 2 A comparison table of segmented pressure ratio functions for a method for determining exhaust pressure of an engine in an embodiment of the present invention;

[0046] Figure 3 This is a control flow block diagram of a method for determining the exhaust pressure of an engine in an embodiment of the present invention.

[0047] Description of reference numerals:

[0048] 10: First equivalent nozzle;

[0049] 11: upstream of the first equivalent nozzle; 12: downstream of the first equivalent nozzle;

[0050] 20: Second equivalent nozzle;

[0051] 21: Upstream of the second equivalent nozzle; 22: Downstream of the second equivalent nozzle. DETAILED DESCRIPTION

[0052] The following is an explanation of the embodiments of the present invention by specific specific examples. Those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. Although the description of the present invention will be introduced in conjunction with the preferred embodiment, this does not mean that the features of this invention are limited to this embodiment. On the contrary, the purpose of introducing the invention in conjunction with the embodiment is to cover other options or modifications that may be extended based on the claims of the present invention. In order to provide a deep understanding of the present invention, the following description will contain many specific details. The present invention can also be implemented without using these details. In addition, in order to avoid confusion or blurring the focus of the present invention, some specific details will be omitted in the description. It should be noted that the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

[0053] It should be noted that in this specification, similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not need to be further defined or explained in subsequent drawings.

[0054] In the description of this embodiment, it should be noted that the terms "upper", "lower", "inner", "bottom", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, or are the orientations or positional relationships in which the inventive product is usually placed when in use. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, they cannot be understood as limitations on the present invention.

[0055] The terms “first”, “second”, etc. are only used for distinguishing descriptions and should not be understood as indicating or implying relative importance.

[0056] In the description of this embodiment, it should be noted that, unless otherwise specified or limited, the terms "disposed," "connected," and "connected" should be understood broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; and internal connections between two components. Those skilled in the art will understand the specific meanings of the above terms in this embodiment based on specific circumstances.

[0057] To make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0058] Example

[0059] This embodiment provides a method for determining the exhaust pressure of an engine, comprising the following steps:

[0060] Obtain the equivalent nozzle flow rate, flow area, and flow coefficient, as well as the upstream temperature and the pressure ratio of the downstream pressure to the upstream pressure. The equivalent nozzle is a nozzle model built based on the exhaust pipe structure. Determine the upstream pressure of the equivalent nozzle based on the flow rate, upstream temperature, flow area, flow coefficient, and pressure ratio. Determine the exhaust pressure based on the upstream pressure of the equivalent nozzle.

[0061] Specifically, the equivalent nozzle refers to a convergent nozzle model established with an exhaust pipe system based on the principles of engineering thermodynamics, where the front end of the minimum cross-section of the equivalent nozzle ( Figure 1 The left end) and the back end ( Figure 1 The right end in FIG is the upstream and downstream of the equivalent nozzle, respectively. Taking the exhaust pipe system with a particulate filter and a turbocharger as an example, in this embodiment, the following is established: Figure 1 In the equivalent nozzle shown, the turbocharger is used as the second equivalent nozzle 20, with the left and right ends of the second equivalent nozzle 20 being the second equivalent nozzle upstream 21 and the second equivalent nozzle downstream 22, respectively. The particulate filter is used as the first equivalent nozzle 10, with the left and right ends of the first equivalent nozzle 11 being the first equivalent nozzle upstream 11 and the left and right ends of the first equivalent nozzle 11 being the first equivalent nozzle downstream 12, respectively. In this case, the exhaust pressure includes the upstream pressures of the first and second equivalent nozzles 10, 20. In this model, the downstream pressure of the first equivalent nozzle 10 is atmospheric pressure, and the downstream pressure of the second equivalent nozzle 20 is the upstream pressure of the first nozzle.

[0062] The flow rate is the flow rate flowing through the equivalent nozzle, which is the sum of the engine intake volume and the fuel injection volume. The engine intake volume can be measured by a flow meter installed in the intake pipe, and the fuel injection volume can be calculated by the intake volume, air-fuel ratio and excess air coefficient (lambda).

[0063] The upstream temperature can be measured by a sensor or calculated by the engine's exhaust temperature model.

[0064] Regarding the acquisition of the flow cross section, if it is a project with a particulate filter, it is fitted according to the carbon accumulation of the particulate filter. If there is no particulate filter, the flow cross section is a constant.

[0065] The flow coefficient of the equivalent nozzle can be calculated and set according to an empirical formula or calibrated according to a specific engine.

[0066] It should be understood that the flow rate, upstream temperature, flow area, flow coefficient, and pressure ratio required to determine the upstream pressure of the equivalent nozzle can be directly obtained using sensors at the corresponding locations, or can be indirectly obtained through computer conversion. After obtaining the above data, the method for calculating the upstream pressure of the equivalent nozzle can be through functional relationships, table lookup after preliminary experiments, or other methods based on the above parameters. This embodiment emphasizes the introduction of the influencing factors of the flow cross-section and flow coefficient into the exhaust pressure calculation strategy. The specific calculation formula and calculation method are not specifically limited in this embodiment. The preferred embodiment is introduced later and will not be repeated here.

[0067] With the above solution, the amount of hot exhaust gas in the cylinder will affect the temperature of the mixture after the intake valve closes. Excessively high mixture temperature can cause compression ignition during the compression stroke of a spark-ignition gasoline engine, causing a sharp increase in the pressure rise rate and damaging the crankshaft connecting rod mechanism. The present invention aims to provide a more accurate exhaust pressure calculation strategy that incorporates the influence of the flow cross-section and flow coefficient to ensure accurate calculation of the hot exhaust gas in the engine cylinder, and thus the fresh charge, providing accurate input for engine fuel consumption, emissions, safety, and power performance.

[0068] In a preferred embodiment, the flow rate, upstream temperature, flow area, flow coefficient and pressure ratio satisfy the following functional relationship, and the upstream pressure of the equivalent nozzle is determined according to the following functional relationship.

[0069]

[0070] Where:

[0071] P1 is the upstream pressure of the equivalent nozzle;

[0072] dm / dt is the flow rate;

[0073] f(T1) is the upstream temperature function obtained based on the upstream temperature and the gas constant of the fuel gas;

[0074] f(μ1) is the flow coefficient function obtained based on the flow coefficient;

[0075] f(F res ) is a flow area function obtained based on the flow area;

[0076] ψ is the piecewise pressure ratio function obtained according to the pressure ratio.

[0077] It should be understood that in the above formula, subscript 1 represents the upstream of the equivalent nozzle, and subscript 0 represents the downstream of the equivalent nozzle.

[0078] Specifically, based on the flow equation (a) for the equivalent nozzle, the back pressure calculation formula can be derived, and then the exhaust pressure calculation strategy can be established.

[0079]

[0080] Among them, the segmented pressure ratio function ψ satisfies the relationship:

[0081]

[0082] Where:

[0083] P0 is the downstream pressure;

[0084] k is the isentropic index.

[0085] More specifically, in the above-mentioned segmented pressure ratio function ψ, k is the isentropic index. For pure combustion products, its linear formula is: ke = 1.365-0.55 / 10000*T. When T changes by 100K, the change in ke is only 0.0055, so ke can be approximately considered a constant. In other words, (2 / k+1) k / k-1 =0.528, when P0 / P1≥0.528,

[0086]

[0087] When P0 / P1≤0.528,

[0088]

[0089] It should be understood that those skilled in the art can also write a calculation program in the controller or terminal to calculate the k value at each temperature to further improve the accuracy of the k value, (2 / k+1) k / k-1 =0.528 is just an example, and this embodiment does not make any specific provision for this.

[0090] Among them, is a single-valued function of the pressure ratio of the upstream and downstream of the equivalent nozzle. After calculating P0, the single-valued function of P1 can be obtained. The relationship between it and the pressure ratio is shown in the figure Figure 2 shown.

[0091] Since the corresponding relationship between ke and pressure ratio is unique after it is determined, it can be written into a table and looked up by pressure ratio. Therefore, when using it, the corresponding relationship between the segmented pressure ratio function and the pressure ratio of the upstream and downstream of the equivalent nozzle can be prepared in advance. Figure 2 The comparison table shown is used to look up the value of the segmented pressure ratio function corresponding to the pressure ratio when actually controlling the engine.

[0092] Furthermore, in the above flow equation (a), ρ is the gas density, the subscript 1 in ρ1P1 represents the upstream of the equivalent nozzle, and similarly 0 represents the downstream of the equivalent nozzle, and dm is the flow rate flowing through the equivalent nozzle within the time dt.

[0093] Based on the above formula (a), as well as PV = mRT and the definition of density ρ = m / V, we can deduce:

[0094]

[0095] Substituting (b) into (a) and simplifying, we have:

[0096]

[0097] In formula (c), R is the gas constant of the fuel gas, which is 287.11 J / (kg*K), and T1 is the temperature upstream of the effective nozzle. Therefore, the pressure P1 upstream of the equivalent nozzle is a function of the flow rate dm / dt flowing through the equivalent nozzle, the upstream temperature T1, the flow coefficient μ, the flow area Fres, and the segmented pressure ratio function, and can be simply expressed as:

[0098]

[0099] That is, the following function formula (e) is obtained, which satisfies the above-mentioned flow rate, upstream temperature, flow area, flow coefficient and segmented pressure ratio function:

[0100]

[0101] Furthermore, the flow coefficient function is f(μ1)=1 / μ1, where μ1 is the flow coefficient of the equivalent nozzle. The flow coefficient is obtained according to the pressure ratio, and the flow coefficient and the pressure ratio satisfy the relationship:

[0102] μ1=a1+a2*π-a3*π 2 ,

[0103] Where π = P0 / P1; coefficients a1, a2, and a3 are calibrated and fitted according to the actual engine performance.

[0104] It should be understood that in order to save computing power, the fitting results can also be made into a calibration table. When the flow coefficient needs to be obtained during the operation of the car, the pre-made calibration table can be queried based on the pressure ratio.

[0105] Taking an existing engine as an example, the flow coefficient and pressure ratio satisfy the relationship:

[0106] μ1=0.49+0.46π-0.08π 2 , where π = P0 / P1.

[0107] That is to say, f(μ1) can also be determined by looking up the pressure ratio table. The method of making the flow coefficient table is the same as the method of the above-mentioned piecewise pressure ratio function ψ, which can be obtained by pre-making a table and then looking up the table.

[0108] The coefficients a1, a2, and a3 are calibrated and fitted according to the actual engine performance. To save computing power, the fitting results can also be made into a calibration table and looked up according to the pressure ratio.

[0109] Furthermore, in a preferred embodiment, the engine is directly calibrated to obtain the flow coefficient.

[0110] In this embodiment, the empirical formula of the flow coefficient has its applicable range, so calibration based on a specific engine is more in line with actual conditions.

[0111] Furthermore, the flow area function is f(F res )=1 / F res , where F res is the circulation area.

[0112] Specifically, if the engine does not have a particulate trap, the flow area function is a fixed value, and the constant can be determined by those skilled in the art according to actual conditions.

[0113] If the engine has a particulate filter, the flow area function value is obtained by consulting a carbon accumulation table based on the accumulated carbon in the particulate filter. The carbon accumulation table is pre-calculated based on the engine's operating time and soot generation. The accumulated carbon is derived using an engine carbon accumulation model, which integrates the engine's operating time and soot generation. The accumulated carbon is negatively correlated with f(Fres); a greater accumulated carbon indicates a smaller flow area. Those skilled in the art can calculate a table corresponding to accumulated carbon before vehicle installation based on actual conditions.

[0114] If the engine has a turbocharger, the value of the flow area function is determined by the turbine nozzle ring angle. It can be fitted according to the turbine nozzle ring angle first, and then obtained by looking up the table according to the turbine nozzle ring angle when in use.

[0115] When the engine has both a turbocharger and a particulate filter, please refer to Figure 1 , the calculation is divided into two stages. First, the pressure upstream of the particulate filter is calculated by the above formula (e) as the input of the downstream pressure of the turbocharger, and then the pressure upstream of the turbocharger is calculated by the above formula (e).

[0116] Furthermore, the upstream temperature function

[0117] Where:

[0118] R is the fuel gas constant;

[0119] T1 is the upstream temperature.

[0120] The upstream temperature T1 can be measured by a sensor or calculated by the engine's exhaust temperature model.

[0121] Furthermore, if the engine is in steady-state operation, the flow rate dm / dt is the intake flow plus the fuel mass flow, where the intake flow is measured by a flow meter installed in the intake pipe, and the fuel mass flow is calculated based on the intake flow, air-fuel ratio, and excess air coefficient.

[0122] If the engine is in dynamic operation, the flow rate dm / dt is determined by dividing the available cycle air mass plus the fuel mass by the cycle time.

[0123] Specifically, dm / dt is the flow rate through the equivalent nozzle, which is the sum of the engine's intake air volume (intake air flow) and the fuel injection volume (fuel mass flow). The engine's intake air volume can be measured by a flow meter installed in the intake manifold, while the fuel injection volume can be calculated from the intake air volume, air-fuel ratio, and excess air coefficient lambda. Dynamic operating conditions refer to acceleration and deceleration.

[0124] Taking the equivalent nozzle established as a turbocharger model as an example, the control diagram of the upstream pressure of the equivalent nozzle is obtained according to the above flow rate, upstream temperature, flow area, flow coefficient and segmented pressure ratio function as shown below: Figure 3 shown.

[0125] According to another specific embodiment of the present invention, an embodiment of the present invention discloses a method for determining the exhaust pressure of an engine. According to the above-mentioned calculation method, if the engine has a particulate filter, a nozzle model is established with the particulate filter as the first equivalent nozzle, and the exhaust pressure includes the pressure before the catalytic converter, which is the upstream pressure of the first equivalent nozzle. If the engine has a particulate filter and a turbocharger, nozzle models are established with the particulate filter and the turbocharger as the first equivalent nozzle and the second equivalent nozzle, respectively, and the exhaust pressure includes the pressure before the catalytic converter and the pressure before the turbine, which is the upstream pressure of the first equivalent nozzle and the pressure before the turbine, respectively.

[0126] Specifically, the downstream pressure of the first equivalent nozzle is atmospheric pressure. The downstream pressure of the second equivalent nozzle is directly obtained via a sensor. If the engine has a particulate filter and a variable geometry turbocharger, in addition to obtaining the downstream pressure of the second equivalent nozzle directly via a sensor, the upstream pressure of the first equivalent nozzle can also be used as the downstream pressure of the second equivalent nozzle.

[0127] Although the present invention has been illustrated and described with reference to certain preferred embodiments thereof, it should be understood by those skilled in the art that the above description is provided as a further detailed description of the present invention in conjunction with specific embodiments thereof, and that the specific implementation of the present invention is not limited to these descriptions. Those skilled in the art may make various changes in form and details, including simple deductions or substitutions, without departing from the spirit and scope of the present invention.

Claims

1. A method for determining the exhaust pressure of an engine, characterized in that The following steps are involved: Obtaining the flow rate, flow area, and flow coefficient of an equivalent nozzle, as well as the upstream temperature and the pressure ratio of the downstream pressure to the upstream pressure of the equivalent nozzle. The equivalent nozzle is a nozzle model established based on the exhaust pipe structure. If the engine has a particulate filter, the flow area is obtained by fitting the carbon accumulation of the particulate filter. determining an upstream pressure of the equivalent nozzle according to the flow rate, the upstream temperature, the flow area, the flow coefficient, and the pressure ratio; The exhaust pressure is determined according to the upstream pressure of the equivalent nozzle; wherein, If the engine has a particulate filter, a nozzle model is established using the particulate filter as a first equivalent nozzle, and the exhaust pressure includes a pressure before the catalytic converter, which is an upstream pressure of the first equivalent nozzle; If the engine has a particulate filter and a turbocharger, nozzle models are established with the particulate filter and the turbocharger as the first equivalent nozzle and the second equivalent nozzle, respectively, and the exhaust pressure includes the pressure before the catalyst pack and the pressure before the turbine. The pressure before the catalyst pack is the upstream pressure of the first equivalent nozzle, and the pressure before the turbine is the upstream pressure of the second equivalent nozzle.

2. The method for determining the exhaust pressure of an engine according to claim 1, characterized in that Determining the upstream pressure includes: Where: P1 is the upstream pressure of the equivalent nozzle; dm / dt is the flow rate; f(T1) is an upstream temperature function obtained according to the upstream temperature and the gas constant of the fuel gas; f(μ1) is a flow coefficient function obtained according to the flow coefficient; f(F res ) is a flow area function obtained according to the flow area; ψ is a segmented pressure ratio function obtained according to the pressure ratio.

3. The method for determining the exhaust pressure of an engine according to claim 2, characterized in that A comparison table is prepared in advance based on the correspondence between the segmented pressure ratio function and the pressure ratio of the upstream and downstream of the equivalent nozzle. When actually controlling the engine, the value of the segmented pressure ratio function corresponding to the pressure ratio is obtained by looking up the comparison table; wherein, The segmented pressure ratio function satisfies the relationship: Where: P0 is the downstream pressure; k is the isentropic index.

4. The method for determining the exhaust pressure of an engine according to claim 2, characterized in that The flow coefficient function is f(μ1)=1 / μ1, Wherein, μ1 is the flow coefficient of the equivalent nozzle.

5. The method for determining the exhaust pressure of an engine according to claim 4, characterized in that The flow coefficient is obtained according to the pressure ratio, and the flow coefficient and the pressure ratio satisfy the relationship: μ1=a1+a2*π-a3*π 2 , Wherein π=P0 / P1, P0 is the downstream pressure; The coefficients a1, a2, and a3 are calibrated and fitted according to the actual engine performance.

6. The method for determining the exhaust pressure of an engine according to claim 2, characterized in that The flow area function is f(F res )=1 / F res , where F res is the flow area; and If the engine does not have a particulate trap, the flow area function is a fixed value; If the engine has a particulate filter, the flow area function is obtained by looking up a carbon accumulation table according to the carbon accumulation of the particulate filter, and the carbon accumulation table is pre-calculated based on the engine's operating time and the soot generated; If the engine has a turbocharger, the flow area function is obtained by looking up a table according to the turbine nozzle ring angle.

7. The method for determining the exhaust pressure of an engine according to claim 2, characterized in that The upstream temperature function Where: R is the fuel gas constant; T1 is the upstream temperature.

8. The method for determining the exhaust pressure of an engine according to claim 2, characterized in that If the engine is in a steady-state operating condition, the flow rate is the intake air flow plus the fuel mass flow, wherein the intake air flow is measured by a flow meter installed in the intake pipe, and the fuel mass flow is calculated based on the intake air flow, the air-fuel ratio, and the excess air coefficient; If the engine is in dynamic operation, the flow rate is determined based on the available cycle intake air mass plus the fuel mass divided by the cycle time.

9. The method for determining the exhaust pressure of an engine according to any one of claims 1 to 8, characterized in that: The downstream pressure of the first equivalent nozzle is atmospheric pressure; The downstream pressure of the second equivalent nozzle is directly obtained by a sensor; or If the engine has a particulate filter and a turbocharger, the downstream pressure of the second equivalent nozzle is the upstream pressure of the first equivalent nozzle.

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